One- and TwoColor Resonant Photoionization Spectroscopy of Chromium Doped Helium Nanodroplets

ABSTRACT: We investigate the photoinduced relaxation dynamics of Cr atoms embedded into superfluid helium nanodroplets. One- and two-color resonant two-photon ionization (1CR2PI and 2CR2PI, respectively) are applied to study the two strong ground state transitions z7P2,3,4 ° ← a 7S3 and y 7P2,3,4 ° ← a 7S3. Upon photoexcitation, Cr * atoms are ejected from the droplet in various excited states, as well as paired with helium atoms as Cr*−Hen exciplexes. For the y7P2,3,4 ° intermediate state, comparison of the two methods reveals that energetically lower states than previously identified are also populated. With 1CR2PI we find that the population of ejected z5P3 ° states is reduced for increasing droplet size, indicating that population is transferred preferentially to lower states during longer interaction with the droplet. In the 2CR2PI spectra we find evidence for generation of bare Cr atoms in their septet ground state (a7S3) and metastable quintet state (a5S2), which we attribute to a photoinduced fast excitation−relaxation cycl